Constant current system



. June 29, 1937.

H. E". YOUN CONSTANT CURRENT Filed July 29,

SYSTEM 5 Sheets-Sheet'l H-nnunu June-29, 1937. H. E. YOUNG 2,085,060

' CONSTANT CURRENT SYSTEM Filed July 29, 1935 5 Sheets-Sheet 2 I nmnmn! unuunn'l June 29, 1937. YOUNG 2,085,060

CONSTANT CURRENT SYSTEM Filed July 29, 1935 5 Sheets-Sheet 3 H. E. YOUNG CONSTANT CURRENT SYSTEM June 29, 1937.

Filed July 29, 1955 5 Sheets-Sheet 4' n e n r mu w June29, 1937. n. E. YOUNG 2,085,060

CONSTANT CURRENT SYSTEM Filed July 29, 1935 I 5 Sheets-Sheet 5 Jawrzion Patented June 29, 1937 QNITED STATES PATENT OFFICE CONSTANT CURRENT SYSTEM Hugh E. Young, Chicagmlll.

Application July 29, 1935', Serial No. 33,706

8 Claims.

The present invention relates primarily to constant current systems, wherein a substantially constant potential is taken from an alternating current supply circuit and is transformed or translated into a substantially constant current in the load circuit. One effective method heretofore employed for transforming from constant potential to constant current has been by the interposition of a monocyclic square between the supply circuit and the load circuit. This monocyclic square is a bridge network comprising inductive and capacitative reactances connected alternately in series. The supply circuit is connected across the input diagonal of this monocyclic square, and the load circuit is connected across the output diagonal of the square. These constant current systems have particular application to street lighting systems in which a variable number of illuminating units are connected in series and form the load circuit. In such a system, it is necessary or desirable to maintain substantially constant current in the load circuit, notwithstanding the fact that the potential of the load circuit will vary with the number of illuminating units effective therein.

One of the principal objects of the invention is to provide an improved monocyclic constant current system characterized by an improved method of and apparatus for regulating the sys tem. in this regard, one of the features is the provision of an improved regulating arrangement which is efiective to control the potential of the supply circuit. One operating difliculty in these monocyclic constant current systems is that the load current in the load circuit varies with changes in the potential of the supply circuit, and this variation is, in many cases, undesirably large. In attempting to avoid this operating difliculty, it has heretofore been proposed to perform a regulating function in the nature of a short-circuiting control on the secondary or output side of the monocyclic square, but this method of regulation has not been satisfactory. My improved method of regulation goes directly to the source of the diificulty, i. e., the

variations in the potential of the supply circuit, and exercises an improved potential regulating control on the supply circuit or on the primary side of the monocyclic square. Another object, characterizing certain embodiments of my invention, is to provide an improved arrangement wherein the operation of the regulating apparatus is made responsive to the current flow in the load circuit.

Another object of the invention is to provide an improved monocyclic constant current system in which the load circuit, the load units and the associated apparatus will be protected from destructive voltages in the event of an accidental interruption of the load circuit.

Other objects and advantages of the invention will appear from the following detail description of certain preferred embodiments thereof. In the accompanying drawings Figures 1, 2, 3, 4 and 5 are circuit diagrams illustrating different embodiments of the invention.

Referring first to the embodiment illustrated in Figure l, the alternating current supply line is represented by the two conductors H, I2, and one or more constant current load circuits are indicated at M, M. In the illustrated arrangement the load circuit I4 is an alternating current circuit and the load circuit I4 is a direct current circuit, each consisting of a conductor connected in series with the several current receiving devices It. These constant current systerns have particular utility for street lighting purposes, and accordingly the receiving units it may be regarded as lamps in a street lighting circuit, although it will be understood that the constant current load circuit might be employed to supply electric furnaces or other devices where constant current is a desideratum. it will be understood that where the load units it are lamps, each lamp will be provided with a com ventional automatic cut-out or short circuiter (not shown) to prevent interruption to the line flow should the lamp burn out or be turned out; and such automatic cut-outs or short-circuiters may also be provided where the load units are other types of devices. It will be seen that with the lamps connected in series, as shown, the resistance, and consequently the load of the line will vary with any increase or decrease of the number of lamps in use.

The transforming device for transforming the substantially constant potential of the supply circuit to the substantially constant current for each load circuit is represented by the monocyclic square, designated IS in its entirety. The latter comprises two inductive reactances l1, l1 and two condensive reactances' l8, l8 connected alternately in series in a bridge network. The alternating current supply line ll, I2 is connected to the primary side, or input diagonal of the monocyclic square, this input diagonal being represented by the two diagonally opposite points l9, 19. The constant current load circuit has connection through conductors 22, 22' with the secondary side or output diagonal of the square, this output diagonal being represented by the diagonally opposite points 2|, 2|. Preferably, the two inductive and the condensive reactances I1, I1 and l8, l8 are each of equal reactance. For proper operation of the system, it is desirable that there be an exact balance of the four reactances. condensers produced in commercial manufacture may vary from the designed value to a certain ex- Inasmuch as the capacity of the" tent, I find it preferable to provide the inductive reactances I I, I1 with several taps, as shown, to provide compensation for differences in the condensers. While I prefer to employ the monocyclic square type of transforming device in my improved constant current system by reason of better full-load efficiency, power factor, apparatus economy, etc., it will be understood that other transforming devices for transforming from constant potential to constant current may be employed between the supply circuit and the load circuit, such as a T-connection or resonating circuits utilizing inductive and condensive reactances.

A transformer 23 is preferably interposed between the monocyclic square I6 and the load, the primary of this transformer being connected with the conductors 22, 22', and the secondary of the transformer being connected with the series load circuit I4. The use of said transformer enables the system to utilize standard condensers I8, I8 in the monocyclic square, while still adapting the resulting current to the proper value for street lighting circuits. In this regard, when the proper balance of the four reactances I1, I1 and I8, I8 is made, the resulting constant current may not be of such value as to give the exact rated lamp current by the use of the normal or standard ratio of the transformer 23. Accordingly, either one or both windings of this transfonner are therefore wound with several taps for additional compensation. The interposition of the transformer 23 between the monocyclic square and the load also serves to limit the rise of voltage across the load circuit in the event of accidental interruption of the load circuit. A further safety device consists of a cut-out 21 connected across the secondary winding of the transformer 23, which cutout functions as a safety device in the event that frequency changes or the destruction or impairment of the regulating .pparatus should cause an abnormal rise in the load voltage. The cut-out 21 may be of the film type in which an insulating film under normal operating conditions renders the device nonconducting but which is broken down or punctured on application of an over voltage causing the device to act as a short circuit. The cut-out will short-circuit the secondary terminals of the transformer 23 on the occurrence of an over voltage, and under this condition normal full current will flow through the short-circuited secondary coil of transformer 23 with no damage to the system. The load may consist of a single alternating current load circuit I4, a single direct current load circuit l4, or a plurality of either or both of these circuits. In the case of the direct current load circuit I4, any suitable arrangement of rectifiers 28, 29 are included between the secondary of the transformer 23 and the load units I5, the illustrated arrangement showing the rectifiers in such relation as to give 'a full-wave rectification. The cut-out 2I functions as a safety device in this direct current load circuit in the same manner that it does in the alternating current load circuit.

The windings of relays 3|, 3| are connected in series in the load circuits I4, I4 to be responsive to current flow therethrough. The contacts 32, 32' of these relays exercise a control over the phase of the voltage supply to the grids of the grid controlled arc rectifier tubes of the regulating apparatus, as I shall presently describe.

Referring now to this regulating apparatus, a variable flux induction transformer 35 is connected to the supply line II, I2. This transformer comprises three windings, namely, a primary winding 31 connected across the supply line, a secondary winding 38 connected in series in the supply line, and a control winding 39 which coacts therewith in a regulating function for regulating the potential on the current supply line. These three windings are preferably mounted on the end and central legs of a transformer core structure 4|, substantially as shown. Provision is made for reversing the connection of the terminals of the secondary winding 38 in the conductor I2 of the supply line, as by throwing a reversible buck or boost switch 44 to one or the other of its two positions, whereby the secondary winding 38 can be connected either in a bucking or boosting relation in the supply line.

The control winding 39 of said transformer 35 is connected to the secondary winding 45 of a saturable core reactor 45. The primary winding 4'! of the reactor 45 is connected through conductors 48' and 49 with the plate circuits of two grid-controlled arc rectifying tubes SI and 52, which are adapted to supply a controlled direct current to said primary winding 41. The anodes of these two tukxes are supplied with alternating current potential through an anode or power transformer 53. The primary winding 54 of this transformer is connected across the supply line H, I2 through conductors 5B and 51. The terminals of the secondary winding 55 are connected through conductors 58 and 59 with the anodes or plates of the tubes 5I and 52. The conductor 48 extending from the primary 4'! of the saturable core reactor 45 has connection with a central tap on the secondary winding 55 of the anode transformer 53. The other conductor 49 leading from the primary winding of the saturable core reactor has connection with a conductor 6| which establishes a cross connection between the filaments of the two tubes. The filaments of the tubes are heated through any filament circuit, not shown. It will be seen from the foregoing that the two tubes perform full-wave rectification and supply a direct current to the primary winding 41 of the saturable core reactor 45. The value of this direct current is dependent upon the conduction period of each tube in each alteration, and the length of this conduction period is determined by the grid potentials which control the time of firing or arcing of the tubes.

One of the features of the invention is the use of a phase shifting or phase splitting method of grid control of these tubes for obtaining substantially instantaneous regulation of the potential supplied to the monocyclic square. This method of grid control employs a phase shifting network comprising a grid transformer 64, a resistor 61 and a reactance 68, 68'. The secondary winding ,66 of the grid transformer has its terminals connected through conductors II and 12 with the grids of the two grid controlled arc rectifying tubes 5I and 52. A conductor 13 extends from a central tap of the secondary winding 66 and connects with the wire 6| which connects the two cathodes of the tubes. The primary winding 65 of the grid transformer has one terminal connected through conductor 15 with a central tap on the primary winding 54 of anode trans-- former 53. Extending from the two end terminals of said latter primary winding 54 are conductors I1 and I8 which form two branch paths both reuniting in conductor I9 which extends to the other terminal of the primary winding 65 of grid transformer 84. The resistor 81 is interposed in series in conductor 11. The reactance 68, 68 is'interposed in series in the other conductor 18. The phase shifting control of the grid voltage is eifected by varying the reactance 88, 68'. This reactance comprises two sections, namely, the'section 88 which is in the form of a variable inductance adapted to respond to the potential of the supply circuit I2, and a second section 68 of fixed reactance which is adapted to be inserted into or out of circuit by the relays 3|, 3| in response to thecurrent flow in the load circuits l4, l4. The variable inductance 88 is preferably in the form of a coil surrounding a movable plunger 8| of iron or other suitable magnetic material, which is movable to different positions within the coil. This plunger is pivotally connected with one end of a lever 82 mounted on an intermediate fulcrum or pivot. 83. Pivotally connected to the other end of said lever is a solenoid core or armature 84 which responds to the magnetic attraction of a coil 85. Said coil is connected in shunt across the supply line II, I! by the conductors 88 and 81. An adjustable tension spring 88 is connected betweenone end of the lever 82 and an adjusting member 89; such as a thumb screw, the latter enabling the spring to be adjusted to exert different degrees of tension on the lever for obtaining the proper normal setting of the two cores 8| and 84, or-for adjusting the apparatus to different ranges of voltage change. Other motion transmitting relations between the two cores 8| and 84 may be adopted, although I regard the lever arrangement illustrated as preferable.

The other section 68 of the inductance in the phase shifting network is adapted to have a shunt placed across the same through conductors 9|, 9 2 and 93 connecting in series with the contacts 32, 32' of the relays 3|, 8| in the load circuits.

Referring now to the operation of the system, an increase of potential in the supply circuit l2 acts through the potential coil to increase the magnetic attraction on the core '84, thereby depressing the other coreBl further into the variable inductance coil 88 and increasing the inductance in the branch circuit 18 of the phase shifting network. Increasing the inductance in this branch circuit connecting, with the primary winding of the grid transformer 84 shifts the grid voltage to an out of phase relationship to the anode voltage, or causes the grid voltage to become more out of phase relative to the anode voltage than it was before this regulating operation. Shifting the phase relationship delays the firingor arcing of the tubes, vlz.. it shortens the conduction period of the tubes. The phase shifting arrangement disclosed enables the phase of the grid voltage to be displaced from zero degrees phase angle. whichvhas a conduction period'of unitv, to a phase angle of -a complete phase splitting relation-which has zero conduction period. Referring again to the regulating operation. it will be assumed that the phase has been shifted to a degree dependent on the rise of potential in the supply line, thereby shortening the conduction period and reducing the flow of direct current through the primary winding 41 of the saturable core reactor 45. This reduces the density of the flux which the direct current ilow sets up in the core of the reactor. Accordingly, the reactance winding 46 of said reactor is enabled to present a higher impedance to current flow through the control winding 38 of the variable "'41 of the saturable core reactor. 45.

flux induction transformer 85. The increased impedance to current flow through the control winding 39 permits a larger proportion of the primary flux to flow in the center leg of core 4|, thus weakening the primary flux density in that part of core 4| surrounded by coil 38. This, in turn, will cause the induced voltage in series coil 38 to be reduced, thus lowering the voltage in the supply ieeder to the monocyclic network. Conversely, if 'thepotential in the supply circuit should decrease from its predetermined normal. the reduced magnetic attraction on the core 84 permits the other core 8| to move outwardly toward a position of lesser inductance within the coil 68. The reduced inductance in the phase shifting network of the grid controlled arc rectifying tubes causes the grid voltage to become more nearly in phase with the anode voltage, thereby increasing the flow of current through the tubes and through the direct current winding The increased flux density thereby created in the core of said reactor reduces the impedance of the winding 46 and its connected control winding 39, with the result of the passage of additional current in coil 39. which in turn increases the primary flux density in that part of core 4| surrounded by coil 38. This in turn will cause the induced voltage in the series coil 38 to be increased. thus increasing the voltage in the supply feeder to the monocyclic network. I

Referring now to the control exercised by the relays 3|. 3| which are interposed in the load circuits l4, H, the construction and arrangement of these relays are such that under normal current flow in the load circuit the relay contact-s32, 32 are closed. Hence, a shunt is normally maintained across the inductance 68' through the circuit 9|, 9?. 93, so that under these conditions the phase shifting network is responsive solely to the changes of inductance which are caused in the variable inductance 68 by the change of potential across the supply line II, I However, in the event that the current flow in either load circuit should be interrupted, as by an accidental break in that circuit, the relay of that circuit is caused to open its respective contacts 32 or 32', thereby opening the short-circuiting shuntaround the inductance 68'. This immediately increases the effective inductance in the branch circuit 18 of the phase shifting network. As previously described. increas ng the inductance in this circuit shifts the grid voltage relatively to the anode voltage and reduces the current flow through the tubes to the winding 41 of the saturab e core reactor 45 which, in turn. causes the variable flux induction transformer 35 to reduce the potential supplied to the monocyclic squares. The inductance 68' is of sufficiently high value so that the phase shift caused by its introduction into the phase shifting circuit will reduce the potential supplied to the monocyclic squares to the point where the dangers incident to a breakin the load circuit are substantially eliminated.

Referring now to the embodiment illustrated in Figure 2, this system is substantially the same as the system of Figure 1, with the exception that the variable induction transformer 35 is omitted and the saturable core reactor 45 has its winding 46 placed in series with the supply circuit. As the potential in the supply circuit l2 increases or decreases from a predetermined normal, the actuation of the cores a4 and BI causes the inductance in the phase shifting network to be increased and decreased so as to control the value of the direct current flowing through the direct current winding 41 of the saturable core reactor 46. This reactor may exercise its potential regulating function on the supply circuit through the instrumentality of the variable flux induction transformer 86, in the same manner described of the embodiment illustrated in Figure 1. However, for the purpose of showing an alternative arrangement, I have illustrated the impedance winding 46 of the reactor as being connected directly in series in the supply circuit II, IL The same general mode of operation follows because increasing the flux density in the core of the reactor by an increased direct current flow through the winding 41 decreases the impedance of the winding 48 for increasing the potential in the supply circuit; and, conversely, reducing the flux density in the core of the reactor increases the impedance in the winding 46 for reducing the potential in the supply circuit. The first of these operations follows upon any tendency of the potential in the supply circuit to increase, and the latter of these operations occurs upon any tendency of the potential to decrease from a predetermined normal. In Figure 2 I have also illustrated an alternating current load circuit I4, and a direct current load circuit I4, either or both of which may be used.

Referring now to the modified embodiment illustrated in Figure 3, this system is substantially the same as the system disclosed in Figure 1, with the exception that the regulating function is made solely responsive to the current flow in the load circuit. The variable inductance apparatus which shifts the phase of the grid potential includes the same arrangement of inductance coil 68, core 8|, lever 82, and core 84. sponds to the magnetic attraction of a solenoid winding 86 which is connected in series in the load circuit. The load circuit may be an alternating current circuit I4 or 'a direct current circuit I4. A rise of current in the load circuit above a predetermined value operates through the solenoid winding 86' and core 84 for increasing the inductance in the phase shifting circuit for reducing the potential of the supply circuit; and conversely a fall of current in the load circuit below a predetermined value operates to increase the potential of the supply circuit. Should more than one load circuit be used, a regulation responding to the current flow in one circuit affords adequate regulation for the other circuits as well. In this embodiment I have also shown the potential regulation as being effected through the medium of a saturable core reactor 45 having its reactance winding 46 connected in series in the supply circuit, although it will beunderstood that, if desired, the saturable core reactor may be arranged to control a variable flux induction transformer 86 for effecting the voltage regulation, as previously described of the embodiment shown in Figure 1.

Referring now to the embodiment illustrated in Figure 4, the potential coil 86 connected across the supply line operates through its core 84 to actuate a lever IOI in accordance with voltage changes in the supply line. This lever constitutes the movable element of a differential regulator, designated I00 in its entirety. Said lever is pivotally mounted at I02, and one end thereof carries a movable contact I03 adapted In this instance, however, the core 84 re-- to establish connection at different points with a resistance I04. The latter resistance is included in a circuit I06, I06 which connects with the terminals of the .primary winding 41 on the saturable core reactor 46. The reactance winding 46 of said reactor may be included directly In the supply circuit II I2, or it may be connected to exercise control over the line potential through the instrumentality of a variable flux induction transformer 86, in the manner previously described in connection with Figure 1. The circuit I06, I06 is connected across a resistor I08 which is included in series in the anode circuit of the grid controlled arc rectifying tubes. The voltage drop across the resistor I08 is conducted through the circuit I06, I06 to the primary winding 41 of the reactor, the current flow from said voltage drop being subject, however, to the value of the variable resistance I04 as determined by the position of the lever IOI. Tension springs I09, I08 connect with the lever III! on opposite sides of the fulcrum I02, and have attachment to adjustable thumb screws III, III or like adjusting means, whereby the tension of these springs can be adjusted. The tension of said springs may be adjusted for graduating the position of the movable contact I06 relatively to the pull of the solenoid core 04 and to the pull of another solenoid core II4 which is pivotally connected to the other end of the lever IOI.

The latter core is movable within a coil I I6, and responds to the current flow therethrough. This coil is connected in series in the anode circuit III of therectifying tubes 6|, 62, said anode circuit comprising the conductor I I So extending from the filaments to the coil I86 and resistor I08, the conductor II 6b extending from the resistor I08 to the coil H6, and the conductor I I6c extending from said latter coil to the central tap of the secondary winding 66 of anode transformer 63. Movable within the solenoid coil I86 is a core I84 which is pivotally connected to one end of the lever I82, fulcrumed at I83. The other end of said lever has the core Ill pivotally connected therewith which operates within the variable inductance coil I68 for varying the inductance of the phase shifting network associated with the rectifying tubes, in substantially the same manner as previously described in connection with Figure 1. Also, as previously described, a spring I88 connected between said lever and an adjustable point of attachment I88 controls the response of the lever I82 to the current flow through the coil I86. In the particular manner in which the lever I82, the two coils I68, I66 and their respective cores I 8| and I84 function in this embodiment, said apparatus constitutes a constant current regulator for the anode circuit H6. For facility of reference, I have designated this constant current regulator I 20 in its entirety.

The load circuits fed from the supply line I I, I2 through the monocyclic squares I6, I6 may be alternating current circuits or direct current circuits, as previously described.

Referring now to the operation of this embodiment, it will be seen that the lever IOI together with the two coils 86 and H6 and their respective cores, constitute a differential regulator for controlling the length of the resistance I04 which is included in the circuit I06, I 06. The position of the lever is differentially responsive to the line voltage impressed on the coil 86, and to the amount of current passing through coil II5 over circuit II6a-II6d. The latter circuit is made a substantially constant-current circuit by virtue of the regulating function of constant-current regulator I20. Any tendency of the current flow through this circuit II6a--I id to rise above a predetermined value operates through the coil I85 and core I84 to actuate lever I82 for increasing the effective inductance of the variable inductance I38 to change the grid phase relation for decreasing the current fiow through the tubes. Conversely, any tendency for the current fiow through this circuit to fall below a predetermined value causes the lever I82 to operate in the reverse direction for decreasing the reactance of the variable inductance I58 to increase the current I flow through the tubes. Thus, a substantially constant current is maintained through the resistor I08, for affording a substantially constant voltage drop across the resistor, which voltage drop supplies the circuit I05, I06 connecting with the saturable core reactor 45. By making the regulator I responsive to the potential in the supply lines I I and I2, any rated amount of constant current can be established by adjustment of regulator I20, which will change the normal position of lever IIlI. Assuming now that this lever has a certain normal position corresponding to a certain potential which it is desired to maintain on the supply circuit, an increase of potential in the supply circuit will operate through the potential coil 85 and core 84 to swing the lever IOI in a counterclockwise direction for interposing additional resistance in the circuitof the primary winding 41 of the saturable core reactor 45. The consequent reduction of current fiow through said primary winding increases the impedance in the reactance winding 46 so as to reduce the volt age in the supply circuit. Conversely, a decrease in voltage across the supply circuit permits the lever IIJI to move in a clockwise direction for reducing the resistance in circuit with the primary winding 41, thereby increasing the current fiow through this winding and decreasing the impedance of the reactance winding 46 for raising the voltage in the supply circuit.

Referring now to the modified arrangement illustrated in Figure 5, in this embodiment the two grid controlled arc rectifying tubes and 52 are connected inversely in the supplycircuit I I, I2 to control the voltage and current fiow to the monocyclic network. The supply line II, I2 is connected to the primary winding'54 of the anode or power transformer 53. The supply circuit is continued from the secondary winding of this transformer through conductors II and I2 to the input diagonal of the monocyclic square I6. The two rectifying tubes 5| and 52 are interposed in reversed parallel relation in one of the conductors II or I2. This reversed relation of the two tubes, wherein one part of the conductor I2 connects to the filament of one tube and the anode of the other, and the continuation of the conductor connects to the anode of the first tube and the filament of the second, enables the two tubes to pass alternating current to the monocyclic network. The phase of the potential applied to the grids is controlled by a phase shifting network which is practically a duplication of that shown in Figure 1, with the exception that the grid transformer 64 is provided with two secondary windings 6'6, 65, one for each grid. The secondary winding 66 is connected through conductors 'II and I3 with the grid and filament respectively of the tube 5|. The other secondary winding 66' is connected through conductors I2 and I3 with the grid and filament respectively of the other tube 52. The two branch paths 1 ,and III of the phase shifting network have the resistor 61 interposed in one of these branch paths, and have the reactances 88, '88 interposed in the other, substantially as previously described. The variable inductance 68 is governed by the motion of the lever 82 in response to the potential impressed on coil 85, which coil is connected. across the supply line conductors Ilf and I2. The section 68 of fixed reactance is connected through conductors 9|, 92 and 93 with the contacts I32, I32 of the relays I3I and I3I'. The windings of the latter relays are connected in series in. the load circuits I4 and I4, this arrangement being similar to that illustrated in Figure 1.

In the operation of this embodiment, all current over thesupply line to the monocyclic network" passes through the tubes 5| and 52, and

hence this current is directly subject to the conduction periods of these tubes. In the event of an objectionable rise of potential in the supply line, the potential coil 85 responds thereto and increases the inductance in the phase shifting network, thereby causing the grid voltage to be-* come more out of phase with the anode voltage and reducing the fiow of current through the tubes. Conversely, a decrease of potential in the supply circuit reduces the inductance in the phase shifting network, causing the grid voltage to become more in phase with the anode voltage and increasing the flow of current through the tubes. With reference to the control which the relays I3I and I3I in the load circuits exercise over the phase shifting network, under normal current conditions in the load circuit, the relay contacts I32, I32 are closed and hence the fixed reactance 68 is shunted so that it has no effect in the network. However, upon an interruption of the current fiow in either load circuit, the relay of that circuit opens its respective contacts and thereby includes the reactance 68' in the network in series with the variable inductance 58. This immediately causes the grid voltages to become more out of phase with the anode voltage and hence reduces the fiow of current through the tubes, reducing the voltage impressed on the monocyclic squares and avoiding dangerous voltages in the load circuits. Where only a single load circuit is fed from the supply circuit the single relay in this load circuit will perform this same controlling operation. The control effected through' the tubes 5| and 52 necessarily controls the voltage impressed on each monocyclic network because the variation in the time of firing of the tubes determines the points in the voltage cycles at which the voltage is conducted through the tubes.

My improved constant-current system has several characteristic features and advantages which are common to all of the embodiments above described. For example, the current in either of the load circuits I4 or I4 is independent of'the load in these circuits. Moreover, the current in the load circuits is directly proportional to the high. The loss in the inductance elements of the monocyclic square. is very low, and the condensers have practically no power loss.

Inasmuch as the secondary current of a monoused to control a number of circuits out of a vault.

While I have illustrated and described what I regard to be the preferred embodiments 01' my invention, nevertheless it will be understood that such are merely exemplary and that numerous modifications and rearrangements may be made therein without departing from the essence of the invention.

I claim:-

1. In combination, an alternating current supply circuit, a substantially constant current load circuit, a monocyclic square connecting said supply circuit with said load circuit, potential regulating means for controlling the potential of saidsupply circuit comprising a saturable core reactor and an electron tube, the conduction period or said electron tube governing the flux density in said reactor, and means responsive to the potential of said supply circuit and to the current in said load circuit for controlling the conduction 5 period of said tube.

2. In combination, an alternating current supply circuit, a substantially constant current load circuit, means for transmitting energy therebetween, an electron tube connected to control the potential of said supply circuit, and means responsive to the potential of said supply circuit and to the current flow in said load circuit for controlling said electron tube.

3. In combination, an alternating current supply circuit, a substantially constant current load circuit, a monocyclic square connect-ing said supply circuit with said load circuit, potential regulating means for controlling the potential of said supply circuit comprising an electron tube characterized by a controllable conduction period, the conduction period of said tube governing said voltage regulating means, and means responsive to the potential of said supply circuit and to the current flow in said load circuit for controlling the conduction period of said tube.

4. In a system of the class described, the com bination of an alternating current supply circuit, a substantially constant current load circuit, a monocyclic square connecting said supply circuit with said load circuit, potential regulating means for controlling the potential oi said supply circuit comprising a saturable core reactor and an electric valve connected therewith, the conduction period of said electric valve governing the flux density of said reactor, and means responsive to the electrical conditionin a part of said system for controlling the conduction period of said valve.

5. In a system of the class described, the combination of an alternating current supply circuit, a substantially constant current load circuit, a monocyclic square connecting said supply circuit with said load circuit, potential regulating means for controlling the potential of said supply circuit, 75 said regulating means comprising a saturable core aoeaoeo reactor and two electron tubes of the grid-controlled arc rectifying type connected therewith to govern the flux density in said reactor, a phase shifting network governing the phase relation 01' the grid potentials applied to said tubes, and means for automatically controlling said phase shifting network to maintain substantially constant potential on said supply circuit.

6. In a system of the class described, the combination 01 a substantially constant potential alternating current supply circuit, a substantially constant current load circuit, a monocyclic square connecting said supply circuit with said load circuit, potential regulating means for said supply circuit comprising a saturable core reactor including a reactance winding and a direct current winding, a direct current circuit connected with said direct current winding, two electron tubes of the grid-controlled arc rectifying type connected with said direct current circuit governing the current flow therethrough for varying the flux density in said reactor, a phase shifting network for varying the phase relation between the grid and anode potentials of said tubes, said phase shifting network being capable of displacing the grid potential substantially 180 degrees out of phase with respect to' the anodev potential, and means for automatically controlling said phase shifting network to maintain substantially constant potential on said supply circuit.

7. In combination, an alternating current supply circuit, a substantially constant current load circuit, means for transmitting energy therebetween, potential regulating means for said supply circuit comprising a variable flux induction transformer, said transformer including a primary winding connected across said supply circuit, a secondary winding connected in series in said supply circuit, and a control winding controlling the flux passing between said primary and secondary windings, a saturable core reactor governing the current flow through said control winding, electric valve means controlling the saturation of said reactor, and means for controlling said electric valve means to maintain substantially constant potential on said supply circuit.

8. In combination, an alternating current supply circuit, a' substantially constant current load circuit, a monocyclic square connecting said supply circuit with said load circuit, potential regulating means for said supply circuit comprising a variable flux induction transformer, said transformer including a core comprising three legs, a primary winding on one of said legs connected across said supply circuit, a secondary winding on another of said legs adapted to be connected in series in said supply circuit, and a control winding on the other of said legs controlling the flux passing through said core between said primary and secondary windings, a switch for connecting said secondary winding in either a bucking or boosting relation in said supply circuit, a saturable core reactor comprising a reactance winding and a direct current winding, said reactance winding being connected with said control winding, two electron tubes of the grid-controlled arc rectifying type for controlling a direct current flow through said direct current winding, a phase shifting network for varying the phase relation between the grid and anode potentials of said tubes, and means for automatically controlling said phase shifting network to maintain substantially constant potential on said supply circuit.

HUGH E. YOUNG. 

